Metal nitride epitaxial layers and films are the basis of many modern electronic devices such as light emitting diodes (LEDs) and power transistors. A nitrogen vacancy (VN) is a point defect affecting chemical bonds between atoms within metal nitrides and is formed by a lack of nitrogen during the production and growth of the metal nitrides. The defects have been shown to be a significant contributor to poor positive (p-type) conductivity in metal nitride compositions, including those used as semiconductors. Typically, nitrogen vacancies have the lowest formation energy in semiconductor materials and may act as single or triple electron donors (VN1+) and (VN3+), respectively. Poor p-type conductivity results in high internal resistance and limits the efficiency and performance of metal nitride semiconductor materials. Therefore, there is a desire to improve p-type conductivity of metal nitride semiconductor materials by reducing nitrogen vacancies (VN1+ and/or VN3+).
It is known that nitrogen vacancies are easily generated in metal nitrides due to the high vapor pressure of nitrogen, and the low efficiency in disassembling NH3. Metal nitrides are often unintentionally doped with nitrogen vacancies during the growth process. As a result, the quality of the grown compositions is diminished, since nitrogen vacancies affect the electrical and optical properties of the metal nitrides. The nitrogen vacancies contribute to the negative (n-type) conductivity of the metal nitrides. N-type conductivity refers to the conductivity associated with donor electrons in a semiconductor, which are functionally equivalent to negative charges.
Efforts to reduce the dominance of n-type conductivity have included doping the materials to increase the p-type conductivity of the material. More specifically, p-type doping agents are incorporated into the metal nitrides in an attempt to counteract or “neutralize” the effect of growth impurities and/or defects, including nitrogen vacancies. P-type doping, however, also generates nitrogen vacancies (VN1+ and/or VN3+) through a self-compensating mechanism.
Nitrogen vacancies are extremely mobile within the lattice structure of metal nitrides. Therefore, it is possible to reduce the density of nitrogen vacancies in the metal nitrides through an annealing process, which diffuses nitrogen atoms into the metal nitride lattice and pushes nitrogen vacancies out of the lattice. High-temperature annealing has shown promise in improving the crystalline structure and electrical conductivity qualities of metal nitrides. Some materials including group III-V metal nitrides (e.g. aluminum nitride, gallium nitride, and indium nitride), however, will decompose under rapid thermal annealing where the pressures range from a vacuum to approximately atmospheric pressure. Thus, there exists a need for a slow high temperature and high pressure (HTHP) annealing process that can be monitored and adjusted is needed to ensure that crystal relaxation and void movement occur without significant nitrogen decomposition.